In a compact disk player (CDP) or a digital video disk player (DVDP), an optical pick-up applies laser energy to a predetermined position on a spiral-shaped disk track, and retrieves the reflected light. A tracking servo directs the light beam to trace the spiral track in all cases, even where the central shaft of the spindle motor driving the disk is eccentric. A focusing servo spaces a pick-up lens from the disk surface at a constant distance, to allow for stability in reading the optical signal.
In a conventional tracking servo, if a mirror warning signal is detected, this is an indication that the disk is out of track. However, when the disk is severely eccentric or deviated, or has many fine scratches, the mirror warning signal is generated too frequently and renders the tracking system unstable, which may cause track jumping.
When a track is selected, for example by a user, a predetermined voltage is applied to a sled motor, which drives a sled, having an optical pickup mounted thereto. The optical pickup is moved to a track position selected by the sled motor, and is focused at the selected track position by the optical pickup lens attached to the sled motor. When a data reproduction command is applied to the sled motor, the lens of the optical pickup may be swayed by a high initial voltage level, or focus drop may occur due to disk defects. Focus loop muting may be applied to prevent the focus drop due to the defect. However, when disk reflectivity is low or if the pickup RF level is reduced, the focus drop cannot be prevented.